A government department mistakenly sent an email to more than 20,000 charities requesting money.

The Charities Commission, which folded into the department of Internal Affairs on July 1, emailed its 25,279 registered charities yesterday asking for overdue tax returns and providing updated banking details.

''We tried to stop the email as soon as we realised they were going to the wrong email group,'' a spokeswoman said.

Volunteer Ian Brown, who does the books for Renewal Trust, said he was confused when he received the email, asking for a payment of $51.11 and quickly began to check his files.

''I didn't know what was going on. These are people from the Government telling me to cough up money that I don't owe,'' he said.

''I rang them and said 'what are you trying to do' and they said 'it is a mistake'.''

Brown said revising the charity's accounts was a job he could have gone without.

''I had to go back and check if I needed to pay it. All they want to do is make life more of a mystery for volunteers.''

The tax return email was only supposed to go out to a few hundred charities, forcing Internal Affairs to issue an apology within the hour.

''You may have received an email from us earlier today, which incorrectly told you that a payment for your charity's annual return was overdue,'' it said.

''If you did, please ignore (and delete) it - we sent it to you by mistake.

''We do apologise for our mistake - and we hope we haven't caused you any undue concern or inconvenience.''

The department has since received ''some feedback'' from charities, and were responding to everyone who had contacted them, the spokeswoman said.

She said the charities didn't have enough time to transfer any funds to the department.

The mistake was the latest blunder by a government department. ACC has been in the spotlight after continuously emailing information to the wrong people, including sending the private details of 6500 ACC clients to Bronwyn Pullar.